I. Field of the Invention
The present invention relates generally to cooling systems for liquid cooled internal combustion engines. More particularly, the present invention relates to such systems where maximum inlet pressure at the coolant pump is maintained.
II. Description of the Relevant Art
The cooling of internal combustion engines has taken many different courses throughout the life of the engine. While the need for cooling was understood, different approaches led to different results.
Some internal combustion engines relied singularly upon air cooling, such as radial airplane engines and the rear-mounted Volkswagen engine of the "Beetle".
However, it was commonly held that liquid cooling was almost universally preferred to air cooling, in that while being more complex, liquid cooling was discovered to be a more efficient method of cooling the engine.
The early Ford Model "T", for example, relied upon a liquid cooling system that utilized a liquid coolant and a radiator, but no coolant pump. The coolant was circulated by a "thermo-siphon" system, whereby the heated coolant naturally flowed upward toward the top of the radiator, was cooled, and naturally flowed downward to the base of the radiator and back into the engine for recirculation.
This approach, however, was not satisfactory, and generally it was found that for maximum efficiency, a coolant pump was necessary, whether the engine being cooled was in a motor vehicle or in an airplane.
Not all coolant systems, however, served all needs. For example, in the automotive engine the cooling system typically has low pressure differentials across the system components and only a small pressure rise across the system is realized, perhaps in the range of four or five PSI. The conventional heat exchanger/pump system works well enough for these purposes.
However, in coolant systems such as that employed in the new generation of aircraft liquid cooled engines the object is to make the overall system light and able to achieve high performance. These engines employ a much higher pressure differential across the heat exchanger in order to minimize the weight and bulk of the cooling system. As a consequence, a much higher pressure rise across the fluid pump, that pressure having an upward end of sixty to seventy-five PSI. (General aviation uses are in the range of thirty to thirty-five PSI, although this pressure is still considerably higher than that found in the conventional automobile.)
The problem primarily encountered in such systems is that maximum pressure at the fluid circulating pump inlet is not acheived due to cavitation causing gas pockets to form around the pump itself. Because gas is highly compressible, if the pocket exists at the pump discharge, as soon as the pump is energized, the gas is compressed to possibly sixty or seventy-five PSI, thus creating a suction at the inlet.
Conversely, it is desirable to operate the system at the maximum temperature while at the maximum pressure because the captured gas will ultimately expand. Accordingly, the object is to operate the system at the temperature of the coolant leaving the engine, not the temperature of the fluid leaving the heat exchanger.
However, prior approaches have failed to solve the problem of providing maximum pressure at the pump inlet while still acheiving the necessary benefits of engine cooling.